1. Field of the Invention
The present general inventive concept relates to a color filter used in a display, and more particularly, to a color filter used in a wide-screen display such as a liquid crystal display (LCD) and a method of fabricating the same.
2. Description of the Related Art
With the advance of PCs (specifically, portable PCs), demand for LCDs (specifically, color LCDs) has increased. However, wide use of LCDs requires a reduction in a high manufacturing cost of the LCDs. Since color filters used in the LCDs are particularly expensive to fabricate, a color filer fabrication cost should be substantially reduced in order to reduce the manufacturing cost of the LCDs.
A color filter fabrication method is an important part of implementing a high image quality of LCDs. Many color filter fabrication methods have been proposed to implement the high image quality of LCDs. Examples of conventional color filter fabrication methods are a pigment dispersion method, a dyeing method, an electrodeposition method, and a printing method.
In the pigment dispersion method, a pigment dispersion photosensitive resin layer is formed on a substrate and then patterned into a monochromic pattern. This process is repeated three times, thereby obtaining R/G/B color filter layers.
In the dyeing method, a glass substrate is coated with a water-soluble high-molecular dyeing material. The dyeing material is then patterned into a predetermined pattern using photolithography, and a colored pattern is obtained by immersing the predetermined pattern into a dyeing solution. This process is repeated three times, thereby obtaining the R/G/B color filter layers.
In the electrodeposition method, a transparent electrode is patterned on a substrate, and a resulting structure is immersed into an electrodeposition coating solution to electrodeposit a first color. This process is repeated three times, thereby forming the R/G/B color filter layers. Finally, the formed R/G/B color filter layers are baked.
In the printing method, a pigment is dispersed into a thermosetting resin to perform a printing process three times, thereby forming the R/G/B color filter layers. The thermosetting resin is thermoset to form a colored layer.
In all the above-described conventional methods, a protection layer is formed on a colored layer that includes the color filter layers.
A common feature of the above-described conventional methods is that the R/G/B colored layers are obtained by repeating an identical process three times. This repetition, however, increases the color filter fabrication cost and reduces a processing yield. In addition, the conventional electrodeposition method is limited in terms of a pattern shape, and thus this method is difficult to apply to a thin film transistor (TFT) LCD. Moreover, since the conventional printing method has a low resolution and smoothness, a fine-pitch pattern is difficult to form using the printing method.
Color filter fabrication methods that attempt to solve the problems described above using an inkjet printing process are described in Japanese Patent Laid-open Publication Nos. SHO 59-75205, SHO 63-235901 and HEI 1-217320. Using these color filter fabrication methods, R/G/B colorant-containing ink is sprayed onto a transparent substrate by the inkjet printing process, and the sprayed ink is dried to form a colored image region. In the color filter fabrication methods using the inkjet printing process, R/G/B pixels can be simultaneously formed, a process of fabricating the color filter can be simplified, and the color filter fabrication cost can be reduced.
In the inkjet printing process for fabricating the color filter, an ink of a selected color is ejected from ink ejection nozzles into each pixel region while an upper surface of a color filter substrate is scanned by an inkjet head, thereby coloring the pixel regions. However, amounts of ink that are ejected from the ink ejection nozzles tends to vary, slightly. Therefore, when a row of pixels is colored using one ink ejection nozzle, neighboring rows of pixels can be colored by different amounts of ink. In this case, color nonuniformity occurs between the neighboring pixel rows. In an effort to reduce the color nonuniformity that results, a method of coloring pixels by performing a scanning operation several times using different nozzles in the respective scanning operations has been proposed. However, since ink ejected in the respective scanning operations may overlap with one another at several portions of each pixel row, the color nonuniformity cannot be sufficiently reduced, unless ink is properly distributed in each scanning operation.
In an effort to solve the problem of overlapping ink and nonuniformity when forming a color filter, U.S. Pat. No. 5,066,512 proposed a method of fabricating a color filter by condensing ink that is ejected using an electrode. However, in this method, when one pixel of a closely-arranged black matrix is electrified by a first electric charge and the other neighboring pixels are electrified by a second electric charge, an insulation problem may occur. In addition, when a finely-ejected ink lands in an undesired region, a resulting defect is impossible to correct.
FIG. 1 illustrates a phenomenon that occurs when using a conventional inkjet system for fabricating a color filter in which ink 15 is made of a mixture of carriers with pigments, dispersants, binders, and monomers. As illustrated in FIG. 1, when the ink 15 is ejected into a pixel (i.e., between a black matrix 12) by an inkjetting process, the ink 15 may overflow on the black matrix 12 on a substrate 10. In more extreme cases, the ink 15 may flow into a neighboring pixel, which causes a bleeding phenomenon.